Just add the columns to the product table, make them varchar(x) date type. You have a choice of leaving them Null is there is no values, or what I like to do is place NA (for Not Applicable) in the column. The NA value helps with not having to remember to add WHERE Columnname Is Not Null or Is Null to queries.

You can see an example of this in the AdventureWorks database from CodePlex.